The present invention relates generally to asymmetrically substituted compounds and, more specifically, to asymmetrically substituted derivatives of bisanhydrohexitols, including isosorbide and isoidide, that may be used as monomers in polymerization reactions.
Isosorbide is a stable, rigid, dihydroxyether derived from glucose by reduction to sorbitol and acid-catalyzed cyclodehydration. It belongs to a class of compounds called bisanhydro-hexitols, other members being isomannide (from mannose) and isoidide (from idose). Such materials are water soluble and harmless and find widespread use in pharmaceuticals and food chemistry. By far the most widely available is isosorbide, which can be obtained from biomass sources via enzyme hydrolysis to make simple hexose sugars and subsequent hydrogenation to make sugar alcohols. Isosorbide is increasingly becoming used as an intermediate and raw material for polymers, additives and stabilizers.
One of the great advantages of isosorbide, unlike its isomers, is that it has two hydroxyl groups with different topographies and chemical reactivity. One —OH is exo and one is endo and as a result they can be selectively esterified and etherified by use of specific chemical reactions under the correct conditions. This invention discloses a range of products and additives in which this idea is exploited to make useful, stereo-defined monomers and polymers based on isosorbide. Incorporation of isosorbide into PET has been shown to raise the Tg of the resulting co-polymer affording a copolymer that has potential as a hot fill bottle resin. However, simple incorporation of isosorbide into PET on a commercial scale has encountered several problems. The secondary hydroxyl groups of isosorbide make it less reactive than the primary hydroxyls of ethylene glycol. This fact coupled with the volatility of isosorbide make it difficult to get high incorporation into PEIT copolymers and leads to complications with the recycle of the ethylene glycol/isosorbide stream generated during polymerization. It is believed that the different reactivities of the two hydroxyl groups of isosorbide also complicate its polymerization chemistry.